A simple question that is very perplexing...

If Venus has had a different past than the Earth, could the Earth become similar to Venus and in effect cause a mass extinction sometime in the future?

That was the simple question. Here is a question that its origins are more transparent: If Venus did not have the dynamics of plate tectonics, could the Earth end up like Venus in the respect that it doesn't have plate tectonics and cause a mass extinction in the far future? If you look at the longevity of Earth in respect to the longevity of the sun, there is one conclusion, but that conclusion does not take into account the longevity of the Earth itself.

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Not likely. Venus' current state is likely the result of a runaway greenhouse effect caused by the boiling off of its oceans. The Earth is not likely to suffer the same fate, even with the current climate change trend, because the Earth has many methods of getting carbon dioxide and water vapor out of the air that Venus didn't; most notably, we have life.

Could Earth end up like Venus? Not really. Venus is 25% closer to the sun than Earth. Even if we did have some sort of runaway greenhouse effect on Earth, our atmosphere's composition is significantly different (much more nitrogen, no sulfuric acid. We also have a magnetic field which protects us from a lot of sun damage. The runaway greenhouse effect hypothesis on Venus would have been caused by the sun getting brighter, rather than any real change on Venus itself.

When climatologists write scary stories about global warming they're talking about a change of a couple degrees at most, not the hundreds of degrees difference that Venus has.

As far as plate tectonics, it's my understanding that active tectonics is needed for a planet to sustain life, because volcanoes return sequestered carbon into the atmosphere. A tectonically dead planet would lose its (non-runaway) greenhouse effect.

Thanks for the best answer to my post. I have a question that delves deeper into the theory that a tectonically dead planet would lose (I am assuming you meant to use the word all at this point) all of the greenhouse effect. Does plate tectonics account for all of the long term and short term carbon dioxide cycles? If not, how much of the carbon dioxide currently (or at any given time) on the surface is due to plate tectonics?

I was hoping you would have read my whole post. It has nothing to do with the greenhouse effect. It has to do with the fact that Venus does not seem to have plate tectonics going on there, but the Earth here does. Maybe I should have just asked: Will the dynamics of the plate tectonics on Earth stop at some time in the future? And, if it does, will it happen before the sun burns the Earth to a crisp?

I ask this because it seems that the evolution of life on Earth has been directly tied to the geological processes that include the plate tectonics.

I do appreciate your answers because reading our banter someone else could have learned something about climate change.

The reason that Venus has no plate tectonics is precisely because of the greenhouse effect. Because all the water's been boiled off, the viscosity of the crust is far too low to allow subduction to happen. So the two questions are closely related.

I'm pretty sure that plate tectonics have little or nothing to do with the amount of water in the crust. The reason continents can move is that they're floating on a sphere of magma. The reason continents do move is that the magma they're floating on has currents. We know that the earth's core is spinning (it's what causes our magnetic field), but Venus may have a core that's not spinning.

Not the motion of the plates themselves, but the formation of subduction zones and volcanoes. The reason why plate tectonics was brought up was because subduction zones are a way of releasing carbon into the atmosphere, and that's what I was responding to.

As for the core, we know that one of two things is the case; either Venus' core and mantle have completely solidified (in which case you wouldn't have any liquid to float on), or Venus' core is at a completely uniform temperature (in which case, there would be no temperature differential to drive convection currents). I'd say it's probably the latter, as pent-up heat still gets released through what are called "resurfacing events."